The first Earl was succeeded by his son, the second Earl. He sat as Member of Parliament for County Tyrone and Dungannon. His son, the third Earl, also represented Dungannon in Parliament. On his early death in 1858, having held the titles for only two months, the peerages passed to his eight-year-old son, the fourth Earl. He also died young and was succeeded by his younger brother, the fifth Earl. He served as a Lord-in-Waiting (government whip in the House of Lords) in the third Conservative administration of Lord Salisbury and was Governor of New Zealand between 1897 and 1904. He also was a member of The Apprentice Boys of Derry Parent Club in Londonderry.

His grandson, the sixth Earl, mainly known as Dan Ranfurly, was well known for his exploits in the Second World War and also served as Governor of the Bahamas from 1953 to 1956. His wife Hermione, Countess of Ranfurly, also became well known for her memoirs of her and her husband's lives during the Second World War and for establishing the organisation which is now known as Book Aid International. They had one daughter but no sons. As of 2014, the titles are held by his fourth cousin, the seventh Earl. He is the great-great-grandson of the Hon. John Knox, third son of the first Earl.

The Hon. William Knox, younger son of the second Earl, was Member of Parliament for Dungannon.

The earldom of Ranfurly, pronounced "Ran-fully", is the last earldom created in the Peerage of Ireland that is still extant. Despite its territorial designation and the fact that it is in the Peerage of Ireland, the earldom (like the UK barony) refers to the village of Ranfurly in Renfrewshire.